The present invention relates to an evaporator, an ice making machine incorporating the evaporator, and a process for making the evaporator.
Automatic ice making machines are well known and are typically found in food and drink service establishments, hotels, motels, sports arenas, and various other places where large quantities of ice are needed on a continuous basis. Some automatic ice making machines produce flaked ice while others produce ice shaped in a variety of configurations, which are commonly referred to as cubes or nuggets.
Automatic ice making machines generally include a refrigeration system having a compressor, a condenser, an evaporator, and an expansion valve. A series of individual ice forming sites are formed on the evaporator and water is supplied to those sites by a water supply system by, for example, trickling or spraying water onto the ice forming site. The run-off of the water is usually recirculated within the water supply. The trickling or spraying methods of supplying water are normally preferred because the methods produce clear ice while the static filled pockets method generally produces white or opaque ice.
Automatic ice making machines are normally controlled as a function of the amount of ice in an ice bin of the ice making machine. When the supply of ice in the ice bin is insufficient, automatic controls cycle the ice making machine through ice production and ice harvest to supplement the supply of ice in the storage portion. In the ice production mode, the refrigeration system operates in a normal manner such that expanding refrigerant in the evaporator removes heat from the series of ice forming sites, freezing the water to form an outwardly growing layer of ice. When the ice thickness reaches a predetermined condition or a specified time period has elapsed, the ice making machine switches to harvest mode.
Typically the harvest mode involves a valve change which directs hot refrigerant gasses to the evaporator. The ice forming locations are heated by the hot refrigerant gasses until the ice in contact with the evaporator begins to thaw. Once the ice falls from the evaporator, it is collected by an appropriate ice bin. When more ice is required, the refrigerant system is switched back to the production mode and the cycle begins again. These cycles continue until there is sufficient ice in the ice bin.
In accordance with one aspect of the invention, an evaporator comprises a refrigerant conduit and front and rear plates sandwiching the refrigerant conduit. The front and rear plates have inner flat portions, each inner flat portion of the front plate facing, but being spaced from, a respective inner flat portion of the rear plate to define a respective spaced portion. The front and rear plates also include a set of first protrusions, each first protrusion on the front plate facing a respective first protrusion on the rear plate to define a respective active cavity. The refrigerant conduit extends through each of the active cavities. The front and rear plates further include a set of second protrusions, each second protrusion on the front plate facing a respective second protrusion on the rear plate to define a respective passive cavity. The refrigerant conduit does not extend through any of the passive cavities. The location of the active and passive cavities are interspersed and separated by respective inner flat portions so as to define a plurality of ice forming sites.
In a preferred embodiment, the evaporator uses a single refrigerant conduit having a serpentine shape. However, a plurality of refrigerant conduits can be used. For example, a first refrigerant conduit can be used for the upper half of the evaporator and a second refrigerant conduit can be used for the lower half of the evaporator. In either case, a portion of at least one of the refrigerant conduits preferably extends through each of the active cavities.
The refrigerant conduit is preferably a pipe having grooves formed along its inner surface so as to increase the inner surface area of the pipe and thereby improve the heat transfer between the refrigerant flowing through the pipe and the ice forming surfaces of the protrusions defining the ice forming cavities. The inner groves preferably run helically along the inner surface of the pipe.
Each active cavity is preferably surrounded by a pair of inactive cavities which are connected to the active cavity by respective spaced portions. The spacing between the inner flat faces defining the respective spaced portions, as measured along a line running perpendicular to the flat faces is preferably between 1 and 2 mm. This is important because if the flat portions abut one another it has been found that corrosion can occur.
It has also been found that spaces between the inner walls of the active cavities and the refrigerant conduit passing through them can lead to corrosion of the protrusions forming the active cavities. This can lead to holes being formed in the protrusions which can allow water to enter the active cavities. If that happens water can freeze and melt during the ice making and ice harvesting cycles and can deform the plate and/or the refrigerant conduit. This decreases the heat transfer between the refrigerant in the refrigerant conduit and the outer surfaces of the active cavities and eventually can block refrigerant from passing through the refrigerant conduit. In order to avoid this problem, it is preferred that the outer surfaces of the refrigerant are pressed against (abut) the inner surfaces of the protrusions except for the area where the spaced portions meet the active cavity.
In the preferred embodiment, each protrusion of the respective pair has an outer flat portion surrounded by a pair of curved portions extending from the outer flat portion to the respective pair of inner flat portions. The refrigerant conduit takes the same form.
In one embodiment, the front and rear plates are connected to one another by an appropriate fastener such as bolts or rivets which extend through elongated slots in the front and rear plates. Because the slots are elongated, and preferably formed at a 45 degree angle with respect to the plane in which the inner flat portions lie, the slots need not be perfectly located in order to ensure that they will overlap allowing for easier assembly of the evaporator.
Each of the front plate and the rear plate preferably includes a plurality of fins, which divide each of the front plate and the rear plate into a plurality of ice forming columns each including a plurality of ice forming sites. The ice forming columns preferably run parallel to one another and perpendicular to the direction that the at least one refrigerant conduit passes through the active cavities.
In another aspect of the invention, an ice making system comprises a refrigerant system for circulating cold refrigerant through an evaporator and a source of water applying liquid water to the evaporator to form ice on the evaporator. The evaporator includes a refrigerant conduit and front and rear plates sandwiching the refrigerant conduit. The front and rear plates have inner flat portions, each inner flat portion of the front plate facing, but being spaced from, a respective inner flat portion of the rear plate to define a respective spaced portion. The front and rear plates also include a set of first protrusions. Each first protrusion on the front plate faces a respective first protrusion on the rear plate to define a respective active cavity. The refrigerant conduit extends through each of the active cavities. The front and rear plates further include a set of second protrusions. Each second protrusion on the front plate faces a respective second protrusion on the rear plate to define a respective passive cavity. The refrigerant conduit does not extend through any of the passive cavities. The locations of the active and passive cavities are interspersed and separated by respective inner flat portions so as to define a plurality of ice forming sites. The source of water applies liquid water to the first and second plates whereby ice is formed at the ice forming sites.
The source of refrigerant can switch between a cooling cycle, in which cooling refrigerant is passed through the refrigerant conduit(s) and ice is formed, and a harvesting cycle, wherein a warming refrigerant is passed through the refrigerant conduit(s) and ice falls off of the ice forming sites and is harvested.
In at least one other aspect of the invention, the front plate or the rear plate or the front plate and the rear plate are formed, in part, by bending a flat plate to include the plurality of fins which divide the plate into a plurality of fins to divide them into a plurality of ice forming columns. Each ice forming column preferably includes a plurality of ice forming sites. To assist in this process, notches are formed on the top and/or bottom edges of the flat plate at locations corresponding to the locations of the fins. The fins are then formed by bending the flat plates in a preferably triangular shape while using the notches to determine where to form the fins.